linq select sum and average into view model

Question

How can I do this in a single select statement?

var data = new CampaignData()
{
    TotalPost = await context.Campaigns.SumAsync(c => c.Posts),
    AveragePost = await context.Campaigns.AverageAsync(c => c.Posts),
    TotalImpression = await context.Campaigns.SumAsync(c => c.Impressions),
    AverageImpressions = await context.Campaigns.AverageAsync(c => c.Impressions),
};

Answer 1

You can group by a constant so you can get the sums and averages. Then use SingleAsync to get the single result.

var data = await (from compaign in context.Compaigns
                  group compaign by 1 into grp
                  select new CampaignData()
                  {
                      TotalPost = grp.Sum(cc => cc.Posts),
                      AveragePost = grp.Average(c => c.Posts),
                      TotalImpression = grp.Sum(c => c.Impressions),
                      AverageImpressions = grp.Average(c => c.Impressions),
                  }).SingleAsync();

Another option is to actually let your asynchronous DB calls run in parallel

var totalPostTask = context.Campaigns.SumAsync(c => c.Posts);
var averagePostTask = context.Campaigns.AverageAsync(c => c.Posts);
var totalImpressionTask = context.Campaigns.SumAsync(c => c.Impressions);
var averageImpressionsTask = context.Campaigns.AverageAsync(c => c.Impressions);

await Task.WhenAll(
    totalPostTask, 
    averagePostTask, 
    totalImpressionTask, 
    averageImpressionsTask);

var data = new CampaignData()
{
    TotalPost = totalPostTask.Result,
    AveragePost = averagePostTask.Result,
    TotalImpression = totalImpressionTask.Result,
    AverageImpressions = averageImpressionsTask.Result,
};

If I had to guess I'd say the single DB call would perform better, but you can always test both options out to see which is better.